With the growth of the IT industry, π-conjugated polymers have been drawing much attention as materials for use in the fields of organic electroluminescence, micro-electronics, electro-optics, opto-electronics and photonics. There has been much effort to use π-conjugated polymers for many types of organoelectronic devices, for example, a memory device, a sensor, a solar cell and a storage battery, because of the fact that polymers generally provide excellent mechanical properties as well as unique functions. But, for π-conjugated polymers to be used in an organoelectronic device, developing an efficient patterning technique is a prerequisite. In the prior art, for forming a pattern of monomolecular materials, chemical vapor deposition (CVD) or sputtering techniques have been used, but those techniques are not applicable to polymeric materials.
In this regard, there were various attempts to provide processes of forming a pattern of π-conjugated polymer and several techniques have been reported so far, such as deposition of the scanning electrochemical microscope (see: A. J. Bard, Anal. Chem. 1989, 61, 132), screening-printing (see: F. Ganier, Science, 1994, 265, 1684), microcontact printing (see: S. Brittain, Phys. World, 1998, 11, 31), micromoding in capillaries (see: J. Rogers, Appl. Phys. Lett. 1998, 73, 294) and soft lithography (see: Y. Xia, Angew. Chem. mnt. Ed. 1998, 37, 550). These techniques, however, have a common drawback of requiring additional precision equipment, so it is very hard to put them into practical use.
Also, photolithography techniques using a photochemical reaction were suggested for patterning π-conjugated polymer. For example, Japanese Laid-Open Publication No. 60-165,786 disclosed a formation of polyacetylene pattern via photopolymerization, wherein an acetylene monomer solution is spin-coated onto a substrate, the coating film is partially exposed to UV light under a photomask, and then subsequently developed to form a desired pattern. However, this process has been revealed defective in that patterns with high resolution cannot be easily obtained since crystallization of acetylene monomer, occurring often during the coating process, makes it difficult to form a film coated evenly. In addition, U.S. Pat. No. 4,528,118 discloses a process for preparing conjugated polymer by using sulfonate polymer as a precursor, which can be converted into a conjugated polymer through thermal elimination. But, this process was inherently intended to form a film, not a pattern so it cannot be a suitable solution for the prior art. U.S. Pat. No. 5,976,284 discloses a process for patterning a conjugated polymer, wherein a photoresist is applied onto a layer of conjugated polymer (e.g. polypyrrole), followed by exposure, developing and selective dry etching, to produce a patterned conducting film. But this process is not considered to be practical because the conjugated polymer is highly restricted in its structure so as to permit the selective etching and finding an optimum etching gas is difficult and requires much time and cost.
Thus, there is a strong need for a convenient and efficient process of forming a pattern of conjugated polymer.